Itraconazole is an important therapeutic agent in the management of serious fungal infections, though adequate serum concentrations are necessary for clinical success. Bioavailability of itraconazole in capsule form has been problematic and is sometimes reduced as much as 50% in AIDS patients with gastric hypoacidity. Itraconazole oral solution (IOS) has improved bioavailability when compared to the capsule formulation and unlike capsules, IOS absorption may not be acid-dependent. This study is an open-label, prospective randomized crossover study in healthy adult volunteers to determine the effect of omeprazole, a gastric acid-suppressing proton pump inhibitor, on peak serum concentrations (Cmax) of IOS. Twenty subjects receive a single dose of IOS 400 mg after an overnight fast on 2 occasions, with at least a 7-day period between doses. Subjects are randomized to receive omeprazole 40 mg nightly for 7 days prior to either IOS dose 1 or 2. Serum samples are obtained immediately prior to IOS dose, and then at 1, 1.5, 2, 2.5, 3, 3.5, 4, 6, and 8 hours post-dose. Concentrations of itraconazole and hydroxyitraconazole (an active metabolite) are determined by HPLC. Data are analyzed using a paired T-test.